RU2753546C2 - Methods for producing air-cured fiber cement products - Google Patents

Abstract

FIELD: cement products.

SUBSTANCE: group of inventions relates to a method for producing air-cured fiber cement products, a cured product and its application. The method for producing air-cured fiber cement products includes stages of: (a) providing cured fiber cement powder by crushing cured fiber cement plates to the particle size from 0.1 to 400 mcm; (b) providing an aqueous fiber cement solution containing water, a binder – Portland cement, cellulose and polyvinyl alcohol fibers, compacted fine-dispersed silicon dioxide and/or a filler – calcium carbonate, and the specified cured fiber cement powder in amount from 5 to 40 wt.% per dry mass of the specified solution; (c) providing a raw fiber cement sheet; (d) pressing the specified sheet under pressure from 180 to 250 kg/cm² for 5 to 15 min; (e) preliminary curing the specified raw fiber cement sheet at 60°C for 1-10 h; (f) air curing the specified raw fiber cement sheet, while providing the air-cured fiber cement product. The group of inventions is developed in independent and dependent claims of the formula.

EFFECT: increased strength, reduced density and water absorption, waste disposal.

11 cl, 22 dwg, 5 tbl, 6 ex

Description

The technical field to which the invention relates

The present invention relates to methods for preparing air-cured fiber cement products. More specifically, the present invention provides methods for making air-cured fiber cement products comprising at least the steps of providing a crushed cured fiber cement material that is a powder and producing an air-cured fiber cement product that uses a crushed cured fiber cement material as one of the raw materials. materials. The present invention also relates to air-cured fiber cement products obtained by these methods, as well as the applications of these fiber cement products in the construction industry.

Background to the invention

Fiber cement material is a composite material usually containing cement, cellulose fibers and at least one of silica sand, synthetic fibers and fillers. It is widely used in construction and can take the form of a variety of products, such as corrugated roofing sheets, small tile sheets (roofing tiles), siding sheets, cladding, slabs, etc.

The cured fiber cement waste material has a chemical composition similar to the corresponding fresh fiber cement products from which the waste is derived, and thus can, and ideally, be recycled and reused. Prior art patent documents US20080168927 and US20080072796 relate to methods for reusing fiber cement waste.

However, the reuse of cured fiber cement waste products, such as out-of-specification finished products, construction waste and / or debris, and the like, remains a major concern. For example, from the known methods of recycling fiber cement waste, it has been found that it is difficult to obtain crushed fiber cement material, i.e. A fiber cement powder made from a cured fiber cement material that can then be used as a raw material for fresh fiber cement products. In addition, there are still no known process indications that are required to produce fresh air-cured fiber cement products from a crushed fiber cement waste material. In fact, attempts so far to use milled waste to produce fresh air-cured fiber cement products have yielded products that do not meet the quality requirements required by national legislation.

More specifically, any attempt in the past to use crushed fiber cement material as one of the raw materials for making fresh air-cured fiber cement products has resulted in increased water absorption of the finished products. This makes these products unusable for various reasons, such as an increased risk of mold, swelling and cracking.

However, reusing fiber cement waste for various new uses remains the main, if not the only, approach to avoid recycling large fiber cement waste streams.

Brief description of the invention

It is an object of the present invention to provide new and improved methods for making fresh air cured fiber cement products using a crushed cured fiber cement waste material as one of the raw materials.

As described above, any past attempts to use crushed fiber cement as one of the raw materials for fresh fiber cement products resulted in increased water uptake in the finished products, rendering these products unsuitable for various reasons such as increased risk of mold, swelling and cracking.

The present inventors have solved this problem by developing an improved process for making fresh air-cured fiber cement products using a crushed fiber cement waste material. More specifically, it has been found that the aqueous fiber cement slurry to be used as a starting material for making fresh air cured fiber cement products should contain from about 5 wt% to about 40 wt% cured crushed fiber cement waste, which can be obtained as explained later in this document. In additional specific embodiments, such a fiber cement slurry comprises from about 5 wt% to about 30 wt% cured crushed fiber cement waste powder, for example, from about 5 wt% to about 15 wt% cured fiber cement powder. In still other specific embodiments, the fiber cement slurry for preparing fresh air cured fiber cement products according to the methods of the present invention comprises less than about 15 wt% cured fiber cement powder prepared according to the methods of the present invention, for example, less than about 10 wt% cured fiber cement powder. more preferably less than about 5% by weight of the cured fiber cement powder. In relation to the above, the unit "wt.%" Refers to the weight percent of the component relative to the total dry weight of the composition, ie. all components except free water.

In fact, the present inventors have observed that by using less than about 40 wt% fiber cement waste in fiber cement slurry to make fresh fiber cement products, fresh water uptake can be reduced or at least maintained at the same level, while density can be reduced. compared to fresh air cured fiber cement products containing no waste.

Thus, using the methods of the present invention, we have discovered a new way of converting fiber cement waste into fresh air-cured products with a low density compared to fresh fiber cement products that do not contain waste, while not affecting the rate of water absorption. Density reduction property remains an important aspect with regard to improving the general applicability of fiber cement products.

In a first aspect, the present invention provides methods for making air-cured fiber cement products comprising at least the steps of:

(a) providing a cured fiber cement powder by crushing the cured fiber cement material;

(b) providing an aqueous fiber cement slurry containing water, cement binder, natural or synthetic fibers and less than about 40 wt.% of the specified cured fiber cement powder;

(c) providing a crude fiber cement sheet, and

(d) air curing said green fiber cement sheet, while providing an air cured fiber cement product.

In specific embodiments of the methods of the present invention, the step of providing an aqueous fiber cement slurry comprises mixing at least water, a cement binder, natural or synthetic fibers, and a cured fiber cement powder such that the cured fiber cement powder is present in the aqueous fiber cement slurry in an amount of from about 5 wt% up to about 35 wt.% based on the dry weight of the specified solution. In additional specific embodiments of the methods of the present invention, the step of providing an aqueous fiber cement slurry comprises mixing at least water, a cement binder, natural or synthetic fibers, and a cured fiber cement powder such that the cured fiber cement powder is present in the aqueous fiber cement slurry in an amount of from about 5 wt. % to about 25 wt.% based on the dry weight of the specified solution. In still further specific embodiments of the methods of the present invention, the step of providing an aqueous fiber cement slurry comprises mixing at least water, a cement binder, natural or synthetic fibers, and a cured fiber cement powder such that the cured fiber cement powder is present in the aqueous fiber cement slurry in an amount of from about 5 wt.% to about 15 wt.% based on the dry weight of the specified solution.

In specific embodiments, the methods of the present invention further comprise the step of compressing the green fiber cement sheet prior to air curing. In additional specific embodiments, the step of pressing the green fiber cement sheet comprises pressing the green fiber cement sheet at a pressure of from about 100 kg / cm² to 300 kg / cm², for example, from about 200 kg / cm² to 300 kg / cm², for example, about 230 kg / cm² ...

In specific embodiments of the methods of the present invention, the step of compressing the green fiber cement sheet comprises compressing the green fiber cement sheet for a period of at least 300 seconds, such as at least 500 seconds, such as at least 600 seconds, or at least 700 seconds. In additional specific embodiments of the present invention, the step of compressing the green fiber cement sheet comprises compressing the green fiber cement sheet for a period of time from about 300 seconds to about 700 seconds.

In specific embodiments of the methods of the present invention, the step of providing a cured fiber cement powder comprises crushing the air cured fiber cement product. In further specific embodiments of the methods of the present invention, the step of providing a cured fiber cement powder comprises crushing the air cured fiber cement product using a pendulum mill.

In a second aspect, the present invention provides an air-cured fiber cement product obtained using the methods of the present invention.

In a third aspect, the present invention provides the use of air-cured fiber cement products obtained by the methods of the present invention as a building material.

Brief description of graphic materials

FIG. 1 shows particle size distribution curves of cement and crushed fiber cement powder obtained by the methods of the present invention. Both the cement samples and the air-cured fiber cement tile samples were milled using a pendulum roller mill from Poittemill Group (FR). The particle size distribution was then measured for both types of samples by dry dispersion laser diffraction at 3 bar using a Malvern MasterSizer 2000. FIG. 2 shows the volume percentages of smaller particles versus particle size.

FIG. 2 shows particle size distribution curves of cement and crushed fiber cement powder obtained by the methods of the present invention. Both the cement samples and the air-cured fiber cement tile samples were milled using a pendulum roller mill from Poittemill Group (FR). The particle size distribution was then measured for both types of samples by dry dispersion laser diffraction at 3 bar using a Malvern MasterSizer 2000. FIG. 3 shows the volume percent of particles versus particle size class.

FIG. 3 shows particle size distribution curves of silica sand and crushed fiber cement powder obtained by the methods of the present invention. Both quartz sand samples and samples of air-cured fiber cement tiles were milled using a pendulum roller mill from Poittemill Group (FR). The particle size distribution was then measured for both types of samples by dry dispersion laser diffraction at 3 bar using a Malvern MasterSizer 2000. FIG. 4 shows the volume percentages of smaller particles versus particle size.

FIG. 4 shows particle size distribution curves of cement and crushed fiber cement powder obtained by the methods of the present invention. Both quartz sand samples and samples of air-cured fiber cement tiles were milled using a pendulum roller mill from Poittemill Group (FR). The particle size distribution was then measured for both types of samples by dry dispersion laser diffraction at 3 bar using a Malvern MasterSizer 2000. FIG. 5 shows the volume percent of particles versus particle size class.

FIG. 5 is a view showing the particle morphology of a crushed fiber cement powder obtained by the methods of the present invention, which has a free-flowing character that is similar to the free-flowing character of cement powder, silica flour, or lime powder.

FIG. 6 and 7 represent density normalized flexural strength (tensile strength at break; MOR) measured 29 days after manufacture, 5 different test pieces (of which the composition of samples 2, 3, 4, 5, 6 is shown in Table 1) and two reference samples (of which the composition of samples 1 and 7 is presented in table 1). The tensile strength at break (MOR; expressed in Pa = kg / m⋅s²) was measured using a UTS / INSTRON device (type 3345; force = 5000 N).

FIG. 8 and 9 represent density normalized flexural strength (tensile strength at break; MOR) measured 7 and 28 days after manufacture, 6 different test specimens (of which the composition of specimens 9, 10, 11, 12, 13 and 14 is in table 3) and two reference samples (of which the composition of samples 8 and 15 is presented in table 3). The tensile strength at break (MOR; expressed in Pa = kg / m⋅s²) was measured using a UTS / INSTRON device (type 3345; force = 5000 N).

FIG. 10 and 11 represent the density measured 7 and 28 days after manufacture, 6 different test samples (of which the composition of samples 9, 10, 11, 12, 13 and 14 is shown in Table 3) and two reference samples (of which the composition of samples 8 and 15 are presented in table 3). The density was measured by saturating the samples for 72 hours with tap water. The weight of the samples was then determined under both saturation and immersion conditions. The samples were then left to dry for 48 hours at approximately 105 ° C. For each of the dried samples, the weight was determined again. The density (X) of each sample was calculated by dividing the dry weight (C) by the difference between the submerged weight (B) and the saturated weight (A) according to the following formula: X = C / (AB).

FIG. 12 shows the water absorption versus time of 3 different test samples (of which the composition of samples 9, 12 and 14 is shown in Table 3) and two reference samples (of which the composition of samples 8 and 15 is shown in Table 3), as measured before pressing. Water uptake was measured using the Carsten test, as further described in this document.

FIG. 13 shows the water absorption versus time of 3 different test samples (of which the composition of samples 9, 12 and 14 is shown in Table 3) and two reference samples (of which the composition of samples 8 and 15 is shown in Table 3), as measured after pressing. Water uptake was measured using the Carsten test, as further described in this document.

FIG. 14 represents density normalized flexural strength (tensile strength; MOR;% relative to sample 16) 6 different test samples (of which the composition of samples 17, 18, 20, 21, 22 and 23 is shown in Table 4) and two reference samples (of which the composition of samples 16 and 19 is presented in table 4). The tensile strength at break (MOR; expressed in Pa = kg / m⋅s²) was measured using a UTS / INSTRON device (type 3345; force = 5000 N).

FIG. 15 represents the density (% relative to sample 16) of 6 different test samples (of which the composition of samples 17, 18, 20, 21, 22 and 23 is shown in table 4) and two reference samples (of which the composition of samples 16 and 19 is shown in table 4 ). The density was measured by saturating the samples for 72 hours with tap water. The weight of the samples was then determined under both saturation and immersion conditions. The samples were then left to dry for 48 hours at approximately 105 ° C. For each of the dried samples, the weight was determined again. The density (X) of each sample was calculated by dividing the dry weight (C) by the difference between the submerged weight (B) and the saturated weight (A) according to the following formula: X = C / (AB).

FIG. 16 shows the water absorption versus time of 3 different test samples (of which the composition of samples 21, 22 and 23 is shown in table 4) and two reference samples (of which the composition of samples 16 and 19 is shown in table 4). Water uptake was measured using the Carsten test, as further described in this document.

FIG. 17 represents the density normalized flexural strength (tensile strength at break; MOR) of 6 different test specimens (of which the composition of specimens 25, 26, 27, 28, 29 and 30 is shown in Table 5) and two reference specimens (of which the composition samples 24 and 31 are presented in table 5). The tensile strength at break (MOR; expressed in Pa = kg / m⋅s²) was measured using a UTS / INSTRON device (type 3345; force = 5000 N).

FIG. 18 represents the density of 6 different test samples (of which the composition of samples 25, 26, 27, 28, 29 and 30 is shown in table 5) and two reference samples (of which the composition of samples 24 and 31 is shown in table 5). The density was measured by saturating the samples for 72 hours with tap water. The weight of the samples was then determined under both saturation and immersion conditions. The samples were then left to dry for 48 hours at approximately 105 ° C. For each of the dried samples, the weight was determined again. The density (X) of each sample was calculated by dividing the dry weight (C) by the difference between the submerged weight (B) and the saturated weight (A) according to the following formula: X = C / (AB).

FIG. 19 shows the water uptake versus time of 6 different test samples (of which the composition of samples 25, 26, 27, 28, 29 and 30 is shown in table 5) and two reference samples (of which the composition of samples 24 and 31 is shown in table 5) , which is measured before pressing. Water uptake was measured using the Carsten test, as further described in this document.

FIG. 20 shows the water absorption versus time of 6 different test samples (of which the composition of samples 25, 26, 27, 28, 29 and 30 is shown in table 5) and two reference samples (of which the composition of samples 24 and 31 is shown in table 5) as measured after pressing. Water uptake was measured using the Carsten test, as further described in this document.

FIG. 21 is a SEM (Scanning Electron Microscopy) image of a sample of an air-cured fiber cement product that contains recycled autoclaved fiber cement waste (characterized by visible white silica sand particles in the product) made according to the methods of the present invention.

FIG. 22 is a SEM (Scanning Electron Microscopy) image of a sample of a fresh air-cured fiber cement product where white silica sand particles — as observed in recycled air-cured products according to the methods of the present invention — are completely absent.

The same reference numbers refer to the same, like, or similar elements in different figures.

Detailed description of the present invention

The present invention will be described with reference to specific embodiments.

It should be noted that the term "comprises" used in the claims should not be interpreted as being limited to the means listed below; it does not exclude other elements or steps. Thus, it should be interpreted as determining the presence of the claimed features, steps or components to which reference is made, but not preventing the presence or addition of one or more other features, steps or components or groups thereof. Thus, the scope of the expression “device comprising means A and B” should not be limited to devices consisting only of components A and B. It means that, with respect to the present invention, the only relevant components of the device are A and B.

Throughout this description, reference is made to "one embodiment" or "an embodiment". Such references indicate that a particular feature described in relation to an embodiment is included in at least one embodiment of the present invention. Thus, appearing of the phrases “in one embodiment” or “in an embodiment” in different places in this description is not necessary, but may mean references to the same embodiment. In addition, particular features or characteristics may be connected in any suitable manner in one or more embodiments, as will be apparent to a person skilled in the art.

The following terms are provided for the sole purpose of contributing to the understanding of the present invention.

In the context of this document, the singular forms both the singular and the plural, unless the context clearly indicates otherwise.

In the context of this document, the terms "consisting", "consists" and "consisting of" are synonymous with the terms "including", "includes" or "containing", "contains", and are inclusive or not limited in any way and do not exclude additional, not listed parts, elements or steps of the method.

Enumeration of a range of numeric values using limit values includes all numeric values and fractional numeric values related to the respective ranges, including the listed limit values.

In the context of this document, the term "about" when referring to measured values such as parameter, magnitude, time duration, etc., encompasses deviations of +/- 10% or less, preferably +/- 5% or less, more preferably + / -1% or less, and even more preferably +/- 0.1% or less from and to some predetermined value to the extent that these deviations are appropriate for implementation in the present invention. It should be understood that the meaning to which the term "about" refers is also specific in itself and preferably disclosed.

The terms “(fiber) cementitious mortar”, “(fiber) cement mortar”, “fiber cement mortar” or “fiber cement mortar”, as set forth herein, generally refer to mortars at least containing water, fibers and cement. Fiber cement mortar, as used in the context of the present invention, can also additionally contain other components, such as, but not limited to, limestone, chalk, quicklime, slaked or hydrated lime, crushed sand, powdered quartz sand, quartz flour, amorphous silicon dioxide, concentrated fine silica powder, microsilica, metakaolin, wollastonite, mica, perlite, vermiculite, aluminum hydroxide, pigments, antifoam agents, flocculants and other additives.

The "fiber (s)" present in the fiber cement slurry as described herein can be, for example, treated fibers and / or reinforcing fibers, both of which can be organic fibers (typically cellulosic fibers) or synthetic fibers (based on polyvinyl alcohol, polyacrylonitrile, polypropylene, polyamide, polyester, polycarbonate, etc.).

The "cement" present in the fiber cement slurry as described herein may be, for example, but not limited to, Portland cement, high alumina cement, ferruginous Portland cement, pozzolanic cement, slag cement, gypsum, calcium silicates formed by treatment in an autoclave, and a combination of individual binders. In more specific embodiments, the cement in the articles of the invention is Portland cement.

In the context of this document, the term "water-permeable" when referring to the water-permeability of the conveyor belt (conveyor belt region) generally means that the material from which the water-permeable belt is made (conveyor belt region) allows water to pass through its structure to a certain extent.

The term "bulk density" as used herein is to be understood as a property of a powder, or granules, or other particulate solid, in particular when referring to mineral components (cement particles, filler particles or silica particles). Bulk density is expressed in kilograms per cubic meter (1 g / ml = 1000 kg / m³) or in grams per milliliter (g / ml), since measurements are carried out with cylinders. It can also be expressed in grams per cubic centimeter (g / cm³). Bulk density is defined as the weight of a specified number of particles of a particular material divided by the total volume that this number of particles occupies. The total volume includes the volume of the particles, the volume of the voids between the particles and the volume of the internal pores. The bulk density of powders, as used herein, is also referred to as the “free settling” or “bulk” density, ie. Bulk density measured after pouring the powder without any additional pressing process.

The bulk density of a powder can be determined by any standard bulk density measurement method known to a person skilled in the art.

For example, the bulk density of a powder can be determined by measuring the volume of a known mass of a sample of powder that may have passed through a sieve in a measuring cylinder (described below as Method A), or by measuring the mass of a known volume of powder that has been poured into a measuring vessel (described below as method B).

Method A. Measurement in a measuring cylinder

Procedure . Pass an amount of powder sufficient to make the dough through a sieve with openings greater than or equal to 1.0 mm, if necessary, to break up agglomerates that may have formed during storage; this must be done carefully to avoid altering the nature of the material. Into a dry measuring cylinder with a volume of 250 ml (labeled with 2 ml), carefully inject, without pressing, approximately 100 g of the test sample (m), weighed with an accuracy of 0.1%. Thoroughly level the powder without pressing, if necessary, and read the apparent volume in the unsettled state (V0) to the nearest marked unit. Calculate the bulk density in (g / ml) using the formula m / V0. In general, repeated definitions are desirable to define this property.

If the density of the powder is too low or too high, so that the test sample has an apparent volume in the unsettled state, or more than 250 ml, or less than 150 ml, it is impossible to use a 100 g sample of the powder. Thus, a different amount of powder should be selected as a test sample so that its apparent volume in the unsettled state is 150-250 ml (apparent volume is greater than or equal to 60% of the total volume of the cylinder); the mass of the test piece is indicated in the expression of results.

For test samples with an apparent volume of 50 ml to 100 ml, a 100 ml cylinder with a 1 ml subdivision can be used; the volume of the cylinder is indicated in the result expression.

Method B. Measurement in a vessel

Device . The device consists of a 100 ml stainless steel cylindrical vessel. Procedure. Pass an amount of powder sufficient to perform the test through a 1.0 mm sieve, if necessary, to break up any agglomerates that may have formed during storage and allow the resulting sample to flow freely into the measuring vessel until it overflows. Gently brush off excess powder from the top of the container. Determine the mass (M0) of the powder to the nearest 0.1% by subtracting the previously determined mass of the empty measuring vessel. Calculate the bulk density (g / ml) using the formula M0 / 100 and record the average of three determinations using three different powder samples.

"(Fiber cement) sheet" or "fiber cement sheet" or "sheet" as used interchangeably herein, and also referred to as a panel or plate, is a horizontal, usually rectangular, fiber cement panel or fiber cement sheet made of fiber cement material. A panel or sheet has two major sides or surfaces, which are the surfaces with the largest surface area. The sheet can be used to give an external surface to walls, both internal and external, to a building or structure, for example in the form of facade slabs, siding, etc.

The present invention provides new and improved methods for making fresh air cured fiber cement products using a crushed cured fiber cement waste material as one of the raw materials.

In particular, the inventors have found that the amount of fiber cement waste used to make fiber cement products is important to improve the performance of the finished product. More specifically, it has been found that the aqueous fiber cement slurry to be used as a starting material for the preparation of fresh fiber cement products should contain less than about 40 wt% fiber cement waste based on the dry matter of said slurry, and preferably from about 5 wt% to about 35 wt% fiber cement waste based on the dry matter of said solution, more preferably from about 5 wt% to about 25 wt% fiber cement waste based on dry matter of said solution, most preferably from about 5 wt% to about 25 wt.% Of fiber cement waste in terms of dry matter of the specified solution. The inventors have observed that by using less than about 40 wt% fiber cement waste in fiber cement slurry to make fresh fiber cement products, the water absorption of fresh air-cured products is reduced or at least maintained at the same level as compared to fresh air-cured products. products that do not contain any fiber cement waste, and the density is reduced. This observation differs from what is usually observed when trying to reduce the density of fiber cement products by known methods, where usually the low density leads to an undesirable increase in water absorption.

The main advantage of making fiber cement sheets or slabs with low densities over conventional (i.e. no waste or recycled) fiber cement products is that the products obtained by the methods of the present invention are lighter than products containing no waste equal to dimensions, and therefore have improved applicability. Applicability includes the ease with which the board is handled and positioned.

In a first aspect, the present invention provides methods for making air-cured fiber cement products comprising at least the steps of:

(a) providing a cured fiber cement powder by crushing the cured fiber cement material;

(b) providing an aqueous fiber cement slurry containing water, cement binder, natural or synthetic fibers and less than about 40 wt.% of the specified cured fiber cement powder;

(c) providing a crude fiber cement sheet, and

(d) air curing said green fiber cement sheet, while providing an air cured fiber cement product.

Units "wt%" refer to the weight percent of the component based on the total dry weight of the composition, ie. all components except free water.

The first step in the methods of the present invention comprises providing a cured fiber cement powder by crushing the cured fiber cement material.

The cured fiber cement material that needs to be crushed is usually waste such as construction waste, production waste from a fiber cement plant, construction site waste, or rejected fiber cement products. Crushed cured fiber cement material, usually in the form of cured fiber cement powder, can be used as a raw material for fresh air cured fiber cement products in which the cured fiber cement powder is reused.

The cured fiber cement powder for use in fresh air cured fiber cement products is preferably, although not necessarily, an air cured crushed fiber cement powder.

Alternatively, the cured fiber cement product crushed to produce cured fiber cement powder may be an autoclave cured crushed fiber cement powder.

In some specific embodiments, crushing of the cured fiber cement material is performed using a pendulum mill. In additional specific embodiments, the methods for making the crushed fiber cement material also include the step of drying the cured fiber cement material by pendulum mill crushing. In still further specific embodiments, the step of drying the hardened fiber cement material during crushing in a pendulum mill is performed by injecting hot air into the pendulum mill during crushing.

In certain embodiments, the cured fiber cement material for use as a starting material for producing crushed cured fiber cement material has a water content of less than or equal to about 10% by weight. In additional specific embodiments, the cured fiber cement material for use as a starting material for producing crushed cured fiber cement material has a water content less than or equal to about 10% by weight, for example, less than or equal to about 8% by weight, for example, less than or equal to about 6 % by weight, for example less than or equal to about 5% by weight.

In some specific embodiments, the cured fiber cement material for use as a starting material for producing crushed cured fiber cement material is an air cured fiber cement material.

Alternatively, the autoclaved fiber cement product can be crushed to form a cured fiber cement powder. The combination of air-cured and autoclave-cured fiber cement product can be crushed, or air-cured fiber cement powder and autoclave-cured fiber cement powder can be combined to form cured fiber cement powder.

One of the most important advantages of the crushed fiber cement powder obtained according to the methods of the present invention is that the particles have a granular, sand-like structure and have a free-flowing character that is similar to the free-flowing character and bulk density (as defined herein) of cement powder, silica flour or lime flour (for example, see Fig. 5). In specific embodiments, the crushed powder obtained by the methods of the present invention is particularly characterized by a bulk density of from 1000 kg / m³ to 1600 kg / m³, and preferably from 1000 kg / m³ to 1300 kg / m³.

Thus, the powder is suitable for reuse in fresh fiber cement products without the need for a major change in the manufacturing process (for example, the Gacek method) to obtain fresh cured fiber cement products, i.e. or air cured or autoclavable fiber cement products.

In addition, the resulting cured fiber cement powder particles of the present invention have a particle size distribution that is similar to the particle size distribution of a cement binder (e.g., cement) or a silicon-containing source (e.g., sand or quartz) or filler material (e.g., CaCO ₃ ). In specific embodiments, the resulting cured fiber cement powder particles have a particle size distribution that is similar to that of cement (eg, see FIGS. 1 and 2). In specific embodiments, the resulting cured fiber cement powder particles have a particle size distribution that is similar to that of a silicon containing source (eg, see FIGS. 3 and 4).

By "matching the particle size distribution" of various materials such as cement, fillers, silica-containing material (eg sand) and crushed fiber cement product, as used herein, it is understood that these materials can be used together in a process to make a fiber cement slurry for obtaining fresh air-cured fiber cement products, in particular using the Gacek method, without the need to significantly change the settings of the method.

Thus, the cured fiber cement powder can replace some of the filler, such as limestone, and / or cement used to make fresh air cured fiber cement sheets. The cured fiber cement powder can replace a portion of the cement used to make the fresh air-cured fiber cement material and / or can replace a portion of the silicon-containing source (e.g., a portion of crushed sand) for autoclaved fiber cement products, and / or can substitute for a portion of the fillers (eg , crushed limestone) used in autoclave cured or air cured fiber cement products.

Preferably, the cured fiber cement material that is provided as a starting material for the crushed cured fiber cement material is provided in pieces with a maximum size of no more than 5 cm, usually rectangular pieces with sides of no more than 3 cm or even no more than 2 cm, before how they are crushed, for example, using a pendulum mill. In this context, a part with a size not exceeding A cm means that the largest particle length is not more than A cm.

FIG. 1-4 show the particle size distributions of crushed cured fiber cement tiles relative to cement particles (FIGS. 1 and 2) and relative to silica particles (FIGS. 3 and 4). Air cured fiber cement tiles, available as Alterna from Eternit NV, Belgium, were first pre-crushed to a size of no more than 2 cm by 2 cm.The total moisture content of the pre-cured fiber cement waste material, in this case air cured fiber cement material, was approximately 5-6% by weight based on dry weight.

% by weight on a dry basis is the difference between the weights of the material as samples and the material dried in a ventilated oven at 105 ° C to constant weight.

This pre-shredded material was fed at a rate of from about 350 kg / hr to about 800 kg / hr into a Poittemill Group (FR) pendulum roller mill, in which the material was crushed at a rotation speed of from about 100 to about 400 rpm. To compensate for the moisture content of the pre-ground material, hot air (at a temperature of about 20 ° C to about 100 ° C) was fed along with the pre-ground material to instantly reduce the moisture of the pre-ground material and the resulting pulverized fiber cement powder.

Thus, a crushed, cured fiber cement material was obtained, the particle size distribution curve of which was obtained by measuring by laser diffraction on the dry dispersed material at 3 bar using a Malvern mastersizer 2000.

This fiber cement powder, obtained by grinding in a pendulum mill, had a good consistency (not flaky or loose), a suitable bulk density (from about 1000 kg / m³ to about 1300 kg / m³) and a good particle size distribution for use in making fresh fiber cement. products. Without limiting to any hypothesis or theory, the inventors believe that the pendulum mill used in the methods of the present invention provides a new and improved crushed fiber cement waste powder, as with this technique the fiber cement waste is squeezed or flattened unlike other techniques. milling, which is usually milled by crushing or grinding.

In certain embodiments, the desired particle distribution of the crushed, cured fiber cement material according to the methods of the present invention can be obtained by grinding the cured fiber cement material in the absence of sand or other source of silica. It also facilitates the use of crushed cured fiber cement material as a good raw material for both air cured and autoclave cured fiber cement waste materials.

In additional specific embodiments, the grinding of the cured fiber cement material is performed in a so-called dry state, i.e. the provided cured fiber cement material is not incorporated into the slurry of liquid (usually water) to facilitate grinding as is the case with some other grinding techniques. The result is a relatively dry, crushed, cured fiber cement material in powder form. This facilitates storage of the intermediate product prior to use, for example, to produce a freshly cured fiber cement waste material, which is a fresh air cured autoclaved fiber cement waste material.

The second step of the methods of the present invention comprises providing an aqueous fiber cement slurry containing water, a cement binder, natural or synthetic fibers, and a cured fiber cement powder. In specific embodiments, the implementation of the fiber cement slurry contains at least 5 wt.% Cured fiber cement powder, preferably at least 10 wt.% Cured fiber cement powder. In further specific embodiments, the implementation of the fiber cement slurry contains preferably less than 40 wt.% Cured fiber cement powder, preferably less than 35 wt.% Hardened fiber cement powder, more preferably less than 20 wt.% Cured fiber cement powder, even less than 15 wt.%.

In additional specific embodiments of the methods of the present invention, the step of providing an aqueous fiber cement slurry comprises mixing at least water, a cement binder, natural or synthetic fibers, and a cured fiber cement powder such that the cured fiber cement powder is present in the aqueous fiber cement slurry in an amount of from about 5 wt. % to about 40 wt%, preferably from about 5 wt% to about 30 wt%, more preferably from about 5 wt% to about 20 wt%, most preferably from about 5 wt% to about 15 wt% % based on the dry weight of the specified solution.

With respect to the foregoing, "wt%" units refer to the weight percent of the component based on the total dry weight of the composition, ie. all components except water.

In the next step of the methods of the present invention, fresh fiber cement materials or products are prepared from a fiber cement slurry that is formed into a so-called crude fiber cement product.

Fiber cement mortar usually contains water, technological and reinforcing fibers, which can be natural organic fibers (usually cellulose fibers) and synthetic organic fibers (polyvinyl alcohol, polyacrylonitrile, polypropylene, polyamide, polyester, polycarbonate, polyethylene, etc.), and the fibers can be surface treated (chemically or mechanically) or not, with synthetic inorganic fibers such as glass fibers, cement such as Portland cement, limestone, chalk, quicklime, slaked or hydrated lime, crushed sand, siliceous sand flour, silica sand, amorphous silica, compacted silica fume, silica fume, metakaolin, wollastonite, mica, perlite, vermiculite, aluminum hydroxide, antifoam agents, flocculants, and other additives such as poorly absorbing water or water repellents. In some cases, it is possible to add coloring additives (for example, pigments) to obtain a fiber cement product, which is a so-called colored mass.

Fiber cement products, also called fiber cement sheets or fiber cement panels, are usually prepared using the well-known Gatschek process, feed method or Magnani process, or suitable combinations thereof.

In specific embodiments, the crude fiber cement products are optionally compressed prior to curing.

In certain embodiments, the optional step of compressing the crude fiber cement product is performed using one or more mechanical presses, including but not limited to one or more nip presses.

In certain embodiments, the optional step of compressing the raw fiber cement product is carried out at a pressure of from about 180 kg / cm² to about 250 kg / cm², such as from about 200 kg / cm² to about 240 kg / cm², such as about 230 kg / cm².

In specific embodiments of the methods of the present invention, the optional step of compressing the raw fiber cement product comprises compressing the raw fiber cement sheet for a period of time from about 5 minutes to about 15 minutes, such as from about 5 minutes to about 10 minutes, such as from about 5 minutes to about 7 minutes, preferably about 6 minutes.

The pressure applied to the wet, i.e. uncured fiber cement sheet, causes an increase in the density of the green fiber cement sheet (for example, see table 2).

The density of fiber cement finished products obtained by the methods of the present invention can range from about 1.0 kg / dm³ to about 2.5 kg / dm³, for example from about 1.3 kg / dm³ to about 2.0 kg / dm³. preferably about 1.5 kg / dm³.

In certain embodiments, the unpressed green fiber cement sheet may have a thickness in the range of about 3 mm to about 25 mm, for example, between about 4 mm and about 20 mm, for example, between about 4 mm and about 12 mm, preferably about 5 mm.

In certain embodiments, the compressed green fiber cement sheet has a thickness in the range of about 2 mm to about 20 mm, for example, between about 3 mm and about 15 mm, for example, between about 3 mm and about 10 mm, preferably about 4 mm.

Finally, the methods of the present invention include the step of air-curing the fiber cement sheet while providing a fresh air-cured fiber cement product.

The "crude" fiber cement product, after being prepared by a sheet-making process such as the Gacek process and pressing, may first be pre-cured in air, after which the pre-cured product is further air-cured until it reaches its final strength.

The fresh green sheets, after receiving, can be stacked with metal sheets sandwiched between the stacked green fiber cement sheets and pressed flat. Alternatively, fresh green sheets can be individually compressed and then folded with metal sheets sandwiched between folded and compressed green fiber cement sheets. The fresh green sheets can be shaped, for example corrugated, prior to folding the intermediate, formed metal sheets sandwiched between the fiber cement sheets. For formed, for example corrugated sheets, the sheets are usually pressed separately.

The pre-curing step can take several hours, for example from about 1 hour to 10 hours, for example from 2 hours to 8 hours, for example from 3 hours to 5 hours, preferably about 4 hours, during which the temperature of the sheets rises due to exothermic reaction of cement hardening. Precuring can occur under controlled conditions by adjusting humidity, temperature, or both.

After the first pre-curing step of air-curing the green sheets folded with the intermediate metal sheets, the sheets can be transferred while removing the metal sheets between the green fiber cement pre-cured sheets. After removing the metal sheets, the pre-cured green fiber cement sheets are further air-cured during a curing step that can take several days, typically 2-4 weeks.

The thickness of the fiber cement finished products obtained using the methods of the present invention can vary from about 4 mm to about 20 mm, for example, from about 7 mm to about 13 mm.

The length and width of fiber cement finished products obtained by the methods of the present invention can range from about 1 meter to about 1.7 meters in width and from about 1 meter to about 3.6 meters in length.

In a further aspect, the present invention provides air cured fiber cement products prepared by the methods of the present invention.

In a further aspect, the present invention provides the use of air-cured fiber cement products obtained by the methods of the present invention as a building material.

An advantage of some embodiments of the present invention is that the resulting air-cured fiber cement sheets are suitable and can be used as corrugated roof cladding, roofing tiles, and other products that require a large amount of cement.

The present invention will now be further illustrated in detail with reference to the following examples.

EXAMPLES

It should be clear that the following examples, provided for illustrative purposes, should not be construed as limiting the scope of the present invention. Although only a few illustrative embodiments of the present invention have been described in detail above, one skilled in the art will readily understand fully that many modifications are possible in the exemplary embodiments without substantially departing from the fundamentally new techniques and advantages of the present invention. Accordingly, all such modifications are intended to be included within the scope of the present invention, which is defined in the following claims and in addition to all equivalents. Additionally, it should be borne in mind that many embodiments may be designed so as not to obtain all of the benefits of some of the embodiments, and the lack of certain benefits should not necessarily be construed as an intention that the embodiment is outside the scope. of the present invention.

Example 1: Preparation of Air Cured Crushed Fiber Cement Powder Made by a Pendulum Mill According to the Methods of the Present Invention

In certain embodiments, the desired particle distribution of the crushed air-cured fiber cement material according to the methods of the present invention can be obtained by grinding the air-cured fiber cement material in the absence of sand or other source of silica. It also facilitates the use of crushed cured fiber cement material as a good raw material for both air cured and autoclave cured fiber cement waste materials.

In additional specific embodiments, the grinding of the cured fiber cement material is performed in a so-called dry state with a moisture content of from about 5% to about 10%, preferably from about 5% to about 6%. The provided cured fiber cement material is thus not introduced into the slurry of liquid (usually water) to facilitate milling as is the case with some other milling techniques. The result is a relatively dry, crushed, cured fiber cement material in powder form. This facilitates storage of the intermediate product prior to use, for example, to produce a freshly cured fiber cement waste material, which is a fresh air cured autoclaved fiber cement waste material.

The cured fiber cement powder obtained by grinding cured fiber cement material according to the methods of the present invention has a particle size distribution as shown, for example, in FIG. 1-4. As can be seen in FIG. 1-4, the particle distribution is similar to that of standard fresh fiber cement feedstocks, such as cement particles, milled silica particles and / or milled lime particles.

In specific embodiments of the methods of the present invention, the cured fiber cement material is fed into the pendulum mill (i.e., for grinding) in pieces with a maximum size of no more than 5 cm, usually in the form of rectangular pieces with sides of no more than 3 cm or even no more than 2 cm. In the context of the present invention, a portion with a size of not more than A cm means that the longest particle length is not more than A cm.

FIG. 1-4 show the particle size distributions of crushed cured fiber cement tiles relative to cement particles (FIGS. 1 and 2) and relative to silica particles (FIGS. 3 and 4). Air cured fiber cement tiles, available as Alterna from Eternit NV, Belgium, were first pre-crushed to a size of no more than 2 cm by 2 cm.The total moisture content of the pre-cured fiber cement waste material, in this case air cured fiber cement material, was approximately 5-6% by weight based on dry weight.

% by weight on a dry basis is the difference between the weights of the material as samples and the material dried in a ventilated oven at 105 ° C to constant weight.

This pre-shredded material was fed at a rate of from about 350 kg / hr to about 800 kg / hr into a Poittemill Group (FR) pendulum roller mill, in which the material was crushed at a rotation speed of from about 100 to about 400 rpm. To compensate for the moisture content of the pre-ground material, hot air (at a temperature of about 20 ° C to about 100 ° C) was fed along with the pre-ground material to instantly reduce the moisture of the pre-ground material and the resulting pulverized fiber cement powder.

Thus, a crushed, cured fiber cement material was obtained, the particle size distribution curve of which was obtained by measuring by laser diffraction on the dry dispersed material at 3 bar using a Malvern mastersizer 2000.

This fiber cement powder, obtained by grinding in a pendulum mill, had a good consistency (not flaky or loose), a suitable bulk density (from about 1000 kg / m³ to about 1300 kg / m³) and a good particle size distribution for use in obtaining fresh fiber cement products.

Example 2: Preparation of Air Cured Fiber Cement Tiles Containing 5 wt% to 10 wt% Air Cured Crushed Fiber Cement Powder Prepared According to the Methods of the Present Invention

The fiber cement powder prepared as described in Example 1 was used to prepare fresh fiber cement tiles, i.e. fresh fiber cement air-cured products.

To obtain fiber cement tiles, the following composition of an aqueous fiber cement mortar is usually used:

- 73-80 wt% cement such as Portland cement

- 3-4 wt% cellulosic fibers (such as unbleached softwood kraft pulp)

- 1.5-1.9 wt.% Polyvinyl alcohol fibers

- 10-18 wt.% Carbon filler (usually limestone)

- and not necessarily a small amount of other additives.

Wt% refers to the weight of the component relative to the total weight of all components except free water, i.e. in terms of dry matter.

A series of 5 test slurry samples were prepared (see table 1 below: samples 2-6) where at least part or all of the carbonaceous filler, or at least part of the cement, or both part of the carbonaceous filler and part of the cement, were replaced with crushed cured fiber cement powder obtained by the milling method explained in Example 1. In addition, 2 reference mortar samples (see table 1 below: samples 1 and 7) were prepared that did not contain any crushed waste powder.

Thus, the following 7 compositions of fiber cement mortar were obtained:

Table 1 - Compositions FC with wt% of samples 1-7 (PVA: polyvinyl alcohol fiber Kuraray A8; cellulose: Solombala UKP 60 ° SR; compacted fine silica: EMSAC 500S Elkem Materials Ltd .; CaCO filler ₃ : Calcitec 2001S, Carmeuse SA; cement: CEMI 42.5N, CBR SA, Lixhe)

The compositions of the fiber cement slurry presented in Table 1 were used to obtain green sheets of fiber cement in a prior art Gachek plant.

Half of the green sheets were pressed at 230 kg / cm² and air cured by subjecting them to curing at 60 ° C for 8 hours and then curing under ambient conditions. The other half of the green sheets were left unpressed and air-cured by subjecting them to curing at 60 ° C for 8 hours and then curing under ambient conditions.

The densities of the reference sample 1 and test samples 3 and 4 (the compositions of which are presented in table 1) were measured for both non-pressed and pressed samples (see table 2).

Table 2 - Densities (g / cm³) of samples 1, 3 and 4, not pressed and pressed

As can be seen from Table 2 above, the density of the fiber cement products containing waste is reduced compared to the control without any waste, for both non-pressed and pressed samples.

The air cured sheets were then cut to appropriate sizes and coated to provide air cured fiber cement tiles.

After 29 days, the formed air-cured sheets were analyzed for their physicomechanical characteristics, i.e. tensile strength at break (MOR; expressed in Pa = kg / m⋅s²). The tensile strength at break (MOR; expressed in Pa = kg / m⋅s²) was measured using a UTS / INSTRON device (type 3345; force = 5000 N).

The water uptake measured by the Carsten test was also determined. The test was carried out under both dry air and moisture saturation conditions (dry air condition is obtained by treating samples in a ventilated oven at 40 ° C for 3 days; moisture saturation conditions are obtained by immersing samples in tap water at room temperature for 3 days and atmospheric pressure).

For each of the air-dried and water-saturated sample, the sample thickness was determined. Then, the Karsten tube was secured to the center of each sample with silicone. After 24 hours, the Karsten tube was filled with demineralized water and closed to prevent evaporation. Water uptake (i.e. the volume of water absorbed from the Karsten tube by the sample) was determined after 1, 2, 4, 6, 8, 24, 32 and 48 hours.

The results are shown in FIG. 6 and 7.

As can be seen from the graphs in FIG. 6 and 7, which represent the density normalized flexural strength (tensile strength at break; MOR) of 5 different test specimens (2, 3, 4, 5, 6, the compositions of which are presented in Table 1) and two reference specimens (1 and 7, the compositions of which are presented in Table 1), it can be concluded that the density normalized flexural strength or tensile strength at break (MOR / d²) is higher in the test samples compared to the reference samples. This means that samples containing crushed fiber cement waste powder in amounts from 5 wt% to 15 wt% obtained according to the methods of the present invention have higher strength than reference samples containing no waste powder.

In addition, based on the results of Karsten's tests (data not shown), it can be concluded that the addition of the fiber cement waste powder according to the present invention in place of cement or filler material does not affect water uptake compared to the reference samples containing no crushed powder. fiber cement waste.

Thus, from the above, it can be concluded that fiber cement products containing from 5 wt.% To 15 wt.% Powder from crushed fiber cement waste obtained by the methods of the present invention have characteristics at least comparable and essentially even better than reference fiber cement products that do not contain any crushed waste powder.

Example 3: Preparation of Air Cured Fiber Cement Tiles Containing 15 wt% to 40 wt% Air Cured Crushed Fiber Cement Powder Prepared According to the Methods of the Present Invention

The fiber cement powder prepared as described in Example 1 was used to prepare fresh fiber cement tiles, i.e. fresh fiber cement air-cured products.

To obtain fiber cement tiles, the following composition of an aqueous fiber cement mortar is usually used:

- 73-80 wt% cement such as Portland cement

- 3-4 wt% cellulosic fibers (such as unbleached softwood kraft pulp)

- 1.5-1.9 wt.% Polyvinyl alcohol fibers

- 10-18 wt.% Carbon filler (usually limestone)

- and not necessarily a small amount of other additives.

Wt% refers to the weight of the component relative to the total weight of all components except free water, i.e. in terms of dry matter.

A series of 6 test slurry samples were prepared (see Table 3 below: Samples 9-14) where at least part or all of the carbonaceous filler, or at least part of the cement, or both part of the carbonaceous filler and part of the cement, were replaced with crushed cured fiber cement powder obtained by the milling method explained in Example 1. In addition, 2 reference mortar samples (see table 3 below: samples 8 and 15) were prepared that did not contain any crushed waste powder.

Thus, the following 8 compositions of fiber cement mortar were obtained:

Table 3 - Compositions FC with wt% of samples 8-15 (PVA: Kuraray A8 polyvinyl alcohol fiber; cellulose: Solombala UKP 60 ° SR; compacted fine silica: EMSAC 500S Elkem Materials Ltd .; CaCO filler ₃ : Calcitec 2001S, Carmeuse SA; cement: CEMI 42.5N, CBR SA, Lixhe)

The compositions of the fiber cement slurry presented in Table 2 were used to obtain green sheets of fiber cement in a prior art Gachek plant. Half of the green sheets were pressed at 230 kg / cm² and air cured by subjecting them to curing at 60 ° C for 8 hours and then curing under ambient conditions. The other half of the green sheets were left unpressed and air-cured by subjecting them to curing at 60 ° C for 8 hours and then curing under ambient conditions.

The air cured sheets were then cut to appropriate sizes and coated to provide air cured fiber cement tiles.

After 7 and 29 days, the formed air-cured sheets were analyzed for their physicomechanical characteristics, i.e. tensile strength at break (MOR).

The tensile strength at break (MOR; expressed in Pa = kg / m⋅s²) was measured using a UTS / INSTRON device (type 3345; force = 5000 N).

The density of the samples was measured by first saturating the samples for 72 hours with tap water. The weight of the samples was then determined under both saturation and immersion conditions. The samples were then left to dry for 48 hours at approximately 105 ° C. For each of the dried samples, the weight was determined again. The density (X) of each sample was calculated by dividing the dry weight (C) by the difference between the submerged weight (B) and the saturated weight (A) according to the following formula: X = C / (A-B).

Finally, the water uptake measured by the Carsten test was determined. The test was carried out under both dry air and moisture saturation conditions (dry air condition is obtained by treating samples in a ventilated oven at 40 ° C for 3 days; moisture saturation conditions are obtained by immersing samples in tap water at room temperature for 3 days and atmospheric pressure).

For each of the air-dried and water-saturated sample, the sample thickness was determined. Then, the Karsten tube was secured to the center of each sample with silicone. After 24 hours, the Karsten tube was filled with demineralized water and closed to prevent evaporation. Water uptake (i.e. the volume of water absorbed from the Karsten tube by the sample) was determined after 1, 2, 4, 6, 8, 24, 32 and 48 hours.

The results are shown in FIG. 8 - 13.

As can be seen from the graphs in FIG. 8 and 9, which represent the density normalized flexural strength (tensile strength at break; MOR) of 6 different test specimens (9, 10, 11, 12, 13 and 14, the compositions of which are presented in Table 3) and two reference specimens ( 8 and 15, the compositions of which are presented in Table 3), it can be concluded that the density normalized flexural strength or tensile strength at break (MOR / d²) is at least comparable and in some cases even higher for the test samples compared to reference samples. This means that samples containing crushed fiber cement waste powder in amounts from 15 wt% to 40 wt%, obtained according to the methods of the present invention, have at least comparable strength to reference samples containing no waste powder.

In addition, as shown in FIG. 10 and 11, the density of test samples 9-14, where part or all of the filler and / or part of the cement was replaced with the crushed fiber cement powder of the present invention, was significantly lower compared to the reference samples containing no waste powder. The density, of course, gradually decreases when more crushed fiber cement powder is added instead of filler and / or cement. This is a very important finding since lower density is directly related to lower product weights, which greatly facilitates the handling, applicability and installation of the products by the end user.

Finally, based on the results of Carsten's tests presented in FIG. 12 and 13, it can be concluded that the addition of 15 wt% air-cured fiber cement waste powder instead of cement or filler material does not affect water uptake compared to reference samples containing no crushed fiber cement waste powder. The addition of air cured fiber cement waste powder in a higher amount, for example 30 wt% or 40 wt% instead of cement or filler material, however, results in increased water uptake compared to reference samples containing no crushed powder. fiber cement waste. The results were observed for both non-pressed (Fig. 12) and compressed (Fig. 13) samples.

Thus, from the above, it can be concluded that fiber cement products containing from 15 wt.% To 40 wt.% Powder from air-cured crushed fiber cement waste obtained by the methods of the present invention have characteristics at least comparable and substantially even better, than reference fiber cement products that do not contain any crushed waste powder.

Example 4: Preparation of Autoclave-Cured Crushed Fiber Cement Powder Made by a Pendulum Mill According to the Methods of the Present Invention

Autoclave cured fiber cement products, obtained as Cedral and Tectiva from Eternit NV, Belgium, were first pre-crushed to a size of no more than 2 cm by 2 cm.Total material moisture based on pre-cured fiber cement waste, in this case air cured fiber cement material, was approximately 5-6% by weight in terms of dry weight.

% by weight on a dry basis is the difference between the weights of the material as samples and the material dried in a ventilated oven at 105 ° C to constant weight.

This pre-shredded material was fed at a rate of from about 350 kg / hr to about 800 kg / hr into a Poittemill Group (FR) pendulum roller mill, in which the material was crushed at a rotation speed of from about 100 to about 400 rpm. To compensate for the moisture content of the pre-ground material, hot air (at a temperature of about 20 ° C to about 100 ° C) was fed along with the pre-ground material to instantly reduce the moisture of the pre-ground material and the resulting pulverized fiber cement powder.

Thus, a crushed, cured fiber cement material was obtained, the particle size distribution curve of which was obtained by measuring by laser diffraction on the dry dispersed material at 3 bar using a Malvern mastersizer 2000.

This fiber cement powder, obtained by grinding in a pendulum mill, had a good consistency (not flaky or loose), a suitable bulk density (from about 1000 kg / m³ to about 1300 kg / m³) and a good particle size distribution for use in making fresh fiber cement. products. Without limiting to any hypothesis or theory, the inventors believe that the pendulum mill used in the methods of the present invention provides a new and improved crushed fiber cement waste powder, as with this technique the fiber cement waste is squeezed or flattened unlike other techniques. milling, which is usually milled by crushing or grinding.

Example 5: Preparation of Air Cured Fiber Cement Tiles Containing 5 wt% to 15 wt% Autoclaved Crushed Fiber Cement Powder Prepared According to the Methods of the Present Invention

Autoclave cured fiber cement waste powders from Cedral and Tectiva fiber cement products prepared as described in Example 4 were used to prepare fresh fiber cement tiles, i.e. fresh fiber cement air-cured products.

To obtain fiber cement tiles, the following composition of an aqueous fiber cement mortar is usually used:

- 73-80 wt% cement such as Portland cement

- 3-4 wt% cellulosic fibers (such as unbleached softwood kraft pulp)

- 1.5-1.9 wt.% Polyvinyl alcohol fibers

- 10-18 wt.% Carbon filler (usually limestone)

- and not necessarily a small amount of other additives.

Wt% refers to the weight of the component relative to the total weight of all components except free water, i.e. in terms of dry matter.

A series of 6 test slurry samples were prepared (see Table 4 below: Samples 17, 18, 20, 21, 22 and 23) where at least part or all of the carbonaceous filler, or at least part of the cement, or as part of the carbonaceous filler and part of the cement was replaced with crushed autoclave-cured fiber cement powder obtained by the grinding method explained in Example 4. In addition, 2 reference mortar samples were prepared (see table 4 below: samples 16 and 19) which did not contain any crushed waste powder cured in an autoclave.

Thus, the following 8 compositions of fiber cement mortar were obtained:

Table 4 - Compositions FC with wt% of samples 16-23 (PVA: Kuraray A8 polyvinyl alcohol fiber; cellulose: Solombala UKP 60 ° SR; compacted fine silica: EMSAC 500S Elkem Materials Ltd .; CaCO filler ₃ : Calcitec 2001S, Carmeuse SA; cement: CEMI 42.5N, CBR SA, Lixhe)

The compositions of the fiber cement slurry shown in Table 4 were used to obtain green sheets of fiber cement in a prior art Gachek plant. Half of the green sheets were pressed at 230 kg / cm² and air cured by subjecting them to curing at 60 ° C for 8 hours and then curing under ambient conditions. The other half of the green sheets were left unpressed and air-cured by subjecting them to curing at 60 ° C for 8 hours and then curing under ambient conditions.

The formed air-cured sheets were analyzed for their physicomechanical characteristics, i.e. tensile strength at break (MOR). The tensile strength at break (MOR; expressed in Pa = kg / m⋅s²) was measured using a UTS / INSTRON device (type 3345; force = 5000 N).

The density of the samples was measured by first saturating the samples for 72 hours with tap water. The weight of the samples was then determined under both saturation and immersion conditions. The samples were then left to dry for 48 hours at approximately 105 ° C. For each of the dried samples, the weight was determined again. The density (X) of each sample was calculated by dividing the dry weight (C) by the difference between the submerged weight (B) and the saturated weight (A) according to the following formula: X = C / (A-B).

Finally, the water uptake measured by the Carsten test was determined. The test was carried out under both dry air and moisture saturation conditions (dry air condition is obtained by treating the samples in a ventilated oven at 40 ° C for 3 days; moisture saturation conditions are obtained by immersing the samples for 3 days in tap water at room temperature and atmospheric pressure).

For each of the air-dried and water-saturated sample, the sample thickness was determined. Then, the Karsten tube was secured to the center of each sample with silicone. After 24 hours, the Karsten tube was filled with demineralized water and closed to prevent evaporation. Water uptake (i.e. the volume of water absorbed from the Karsten tube by the sample) was determined after 1, 2, 4, 6, 8, 24, 32 and 48 hours.

The results are shown in FIG. 14 - 16.

As can be seen from the graph in FIG. 14, which represents the density normalized flexural strength (tensile strength at break; MOR) of 6 different test specimens (17, 18, 20, 21, 22 and 23, the compositions of which are presented in Table 4) and two reference specimens (16 and 19, the compositions of which are presented in Table 4), it can be observed that the density normalized flexural strength or tensile strength at break (MOR / d²) of the test samples does not differ much from the MOR / d² of the reference samples. This means that samples containing crushed fiber cement waste powder in amounts from 5 wt% to 15 wt% obtained according to the methods of the present invention have comparable mechanical strength relative to reference samples containing no waste powder.

In addition, as shown in FIG. 15, the density of the test samples 17, 18, 20, 21, 22 and 23, where part or all of the filler and / or part of the cement was replaced with the autoclaved crushed fiber cement powder of the present invention, was significantly lower compared to the reference samples containing no powder from waste. The density, of course, gradually decreases when more crushed fiber cement powder is added instead of filler and / or cement. This is a very important finding since lower density is directly related to lower product weights, which greatly facilitates the handling, applicability and installation of the products by the end user.

Finally, based on the results of Carsten's tests presented in FIG. 16, it can be concluded that the addition of 5 wt% to 10 wt% autoclaved fiber cement waste powder instead of cement or filler material has no significant effect on water uptake compared to reference samples containing no powder. from crushed fiber cement waste.

Thus, from the above, it can be concluded that fiber cement products containing from 5 wt.% To 15 wt.% Powder from autoclaved crushed fiber cement waste obtained by the methods of the present invention have significantly better characteristics than the reference fiber cement products, not containing any powder from crushed waste. Of course, the mechanical strength and water absorption of air-cured fiber cement products containing crushed waste powder does not change compared to air-cured fiber cement products that do not contain waste, while density is significantly reduced for products containing waste relative to those that do not. contain waste.

Example 6: Preparation of Air Cured Fiber Cement Tiles Containing 20 wt% to 40 wt% Autoclaved Crushed Fiber Cement Powder Prepared According to the Methods of the Present Invention

Autoclave cured fiber cement waste powders from Cedral and Tectiva fiber cement products prepared as described in Example 4 were used to prepare fresh fiber cement tiles, i.e. fresh fiber cement air-cured products.

To obtain fiber cement tiles, the following composition of an aqueous fiber cement mortar is usually used:

- 73-80 wt% cement such as Portland cement

- 3-4 wt% cellulosic fibers (such as unbleached softwood kraft pulp)

- 1.5-1.9 wt.% Polyvinyl alcohol fibers

- 10-18 wt.% Carbon filler (usually limestone)

- and not necessarily a small amount of other additives.

Wt% refers to the weight of the component relative to the total weight of all components except free water, i.e. in terms of dry matter.

A series of 6 test slurry samples were prepared (see Table 5 below: Samples 25-30), where at least part or all of the carbonaceous filler, or at least part of the cement, or both part of the carbonaceous filler and part of the cement, were replaced with crushed an autoclave cured fiber cement powder obtained by the milling method explained in Example 4. In addition, 2 reference solution samples (see table 5 below: samples 24 and 31) were prepared that did not contain any autoclave cured crushed waste powder.

Thus, the following 8 compositions of fiber cement mortar were obtained:

Table 5 - FC compositions with wt% samples 24-31 (PVA: polyvinyl alcohol fiber Kuraray A8; cellulose: Solombala UKP 60 ° SR; compacted fine silica: EMSAC 500S Elkem Materials Ltd .; CaCO filler ₃ : Calcitec 2001S, Carmeuse SA; cement: CEMI 42.5N, CBR SA, Lixhe)

The compositions of the fiber cement slurry presented in Table 5 were used to obtain green sheets of fiber cement in a prior art Gachek plant. Half of the green sheets were pressed at 230 kg / cm² and air cured by subjecting them to curing at 60 ° C for 8 hours and then curing under ambient conditions. The other half of the green sheets were left unpressed and air-cured by subjecting them to curing at 60 ° C for 8 hours and then curing under ambient conditions.

The formed air-cured sheets were analyzed for their physicomechanical characteristics, i.e. tensile strength at break (MOR). The tensile strength at break (MOR; expressed in Pa = kg / m⋅s²) was measured using a UTS / INSTRON device (type 3345; force = 5000 N).

The density of the samples was measured by first saturating the samples for 72 hours with tap water. The weight of the samples was then determined under both saturation and immersion conditions. The samples were then left to dry for 48 hours at approximately 105 ° C. For each of the dried samples, the weight was determined again. The density (X) of each sample was calculated by dividing the dry weight (C) by the difference between the submerged weight (B) and the saturated weight (A) according to the following formula: X = C / (A-B).

Finally, the water uptake measured by the Carsten test was determined. The test was carried out under both dry air and moisture saturation conditions (dry air condition is obtained by treating the samples in a ventilated oven at 40 ° C for 3 days; moisture saturation conditions are obtained by immersing the samples for 3 days in tap water at room temperature and atmospheric pressure).

For each of the air-dried and water-saturated sample, the sample thickness was determined. Then, the Karsten tube was secured to the center of each sample with silicone. After 24 hours, the Karsten tube was filled with demineralized water and closed to prevent evaporation. Water uptake (i.e. the volume of water absorbed from the Karsten tube by the sample) was determined after 1, 2, 4, 6, 8, 24, 32 and 48 hours.

The results are shown in FIG. 17 - 20.

As can be seen from the graphs in FIG. 17, which represents the density normalized flexural strength (tensile strength at break; MOR) of 6 different test specimens (17-22, the compositions of which are presented in Table 5) and two reference specimens (16 and 23, the compositions of which are presented in Table 5) ), it can be concluded that the density normalized flexural strength or tensile strength at break (MOR / d²) is higher for the test specimens compared to the reference specimens, especially when the specimens are compressed. This means that samples containing crushed fiber cement waste powder in amounts from 20 wt% to 40 wt%, obtained according to the methods of the present invention, have higher strength than reference samples containing no waste powder. The best results were obtained when the samples were compressed.

In addition, as shown in FIG. 18, the density of test samples 17-22, where part or all of the filler and / or part of the cement was replaced with the autoclaved crushed fiber cement powder of the present invention, was significantly lower compared to the reference samples 16 and 23, which did not contain any waste powder. The density, of course, gradually decreases when more crushed fiber cement powder is added instead of filler and / or cement. This effect was observed for both pressed and non-pressed samples when compared respectively with the corresponding pressed and non-pressed reference samples. This is a very important finding since lower density is directly related to lower product weights, which greatly facilitates the handling, applicability and installation of the products by the end user.

Finally, based on the results of Carsten's tests presented in FIG. 19 and 20, it can be concluded that the addition of 20 wt% autoclave cured fiber cement waste powder instead of cement or filler material does not affect water uptake compared to reference samples containing no crushed fiber cement waste powder. The best results are obtained when the samples are compressed.

The addition of air cured fiber cement waste powder in a higher amount, for example 30 wt% or 40 wt% instead of cement or filler material, however, results in increased water uptake compared to reference samples containing no crushed powder. fiber cement waste.

Thus, from the above, it can be concluded that fiber cement products containing from 15 wt.% To 40 wt.% Powder from crushed fiber cement waste obtained by the methods of the present invention, including the stage of pressing before the stage of curing, have characteristics comparable to fiber cement products, not containing any powder from crushed waste, and have characteristics significantly better than non-compressed fiber cement products containing the same amount of crushed waste.

From images of air cured products made as described in these examples, it can be seen that these products contain autoclaved fiber cement waste. Of course, autoclave-only material typically contains white silica sand particles, with silica sand particles also present in recyclable air-cured products prepared according to the methods of the present invention (see FIG. 20), but which are not present in fresh air-cured products. products (see Fig. 21).

It is understood that although preferred embodiments and / or materials have been contemplated for making the embodiments according to the present invention, various modifications or changes may be made without departing from the scope and spirit of the present invention.

Claims (17)

1. A method for producing air-cured fiber cement products, comprising at least the steps: (a) providing a cured fiber cement powder by crushing the cured fiber cement tiles to a particle size of 0.1 to 400 microns; (b) providing an aqueous fiber cement slurry containing water, a binder - Portland cement, cellulose and polyvinyl alcohol fibers, compacted fine silica and / or filler - calcium carbonate, and said hardened fiber cement powder in an amount of from 5 to 40 wt.% on a dry basis the mass of the specified solution; (c) providing a crude fiber cement sheet; (d) pressing said green fiber cement sheet under a pressure of 180 to 250 kg / cm ² for 5 to 15 minutes; (e) pre-curing the specified green fiber cement sheet at 60 ° C for 1-10 hours; and (f) air curing said green fiber cement sheet, while providing an air cured fiber cement product. 2. A method according to claim 1, characterized in that said step (b) of providing an aqueous fiber cement solution comprises mixing at least water, a binder - Portland cement, cellulose and polyvinyl alcohol fibers, compacted finely dispersed silicon dioxide and / or filler - calcium carbonate, and cured fiber cement powder, so that the cured fiber cement powder is in an aqueous fiber cement solution in an amount of from 5 to 35 wt.% based on the dry weight of the specified solution. 3. A method according to any one of claims. 1 or 2, characterized in that said step (b) of providing an aqueous fiber cement slurry comprises mixing at least water, a binder - Portland cement, cellulose and polyvinyl alcohol fibers, compacted fine silica and / or a filler - calcium carbonate, and a hardened fiber cement powder, so that the cured fiber cement powder is in an aqueous fiber cement solution in an amount of 5 to 15 wt.%, based on the dry weight of said solution. 4. A method according to any one of claims. 1-3, characterized in that said pressing said green fiber cement sheet comprises pressing said green fiber cement sheet by means of at least one or more mechanical presses. 5. The method according to any one of claims. 1-4, characterized in that said pressing said green fiber cement sheet comprises pressing said green fiber cement sheet by means of at least one or more pressing presses. 6. The method according to any one of claims. 1-5, wherein said step (a) of providing the cured fiber cement powder comprises grinding the air cured fiber cement product. 7. A method according to any one of claims. 1-5, wherein said step (a) of providing the cured fiber cement powder comprises grinding the autoclaved fiber cement product. 8. The method according to any one of claims. 1-7, characterized in that said step (a) of providing the cured fiber cement powder comprises grinding the cured fiber cement product with a pendulum mill. 9. Cured in air fiber cement product obtained by the method according to any one of paragraphs. 1-8. 10. The air-cured fiber cement product of claim 9, which is a corrugated fiber cement sheet. 11. The use of air-cured fiber cement product according to any one of paragraphs. 9 or 10 as a building material.

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